Crimping of textile fibres



United States Patent 3,300,831 CRIMPING 0F TEXTILE FIBRES John Parker, Cwmbran, Monmouthshire, Kazimierz Wiktor Mieszkis, Abergavenny, Monmouthshire, and Dennis Anthony Dyer, Cheltenham, Gloucester, England,

assignors to British Nylon Spinners Limited, Pontypool,

England No Drawing. Filed June 14, 1963, Ser. No. 287,805

2 Claims. (Cl. 28-72) This invention relates to the crimping of textile fibres, which expression includes continuous filaments, and particularly to a method and apparatus for the treatment of such fibres in order to impart an improved crimp thereto.

One method and apparatus for imparting crimp to textile fibres, such as polyamide fibres for example, requires that a sliver of staple fibres or a bundle or tow of continuous filaments, hereinafter referred to as a tow, is, by being passed through a feed means in the form of a pair of driven nip rollers, forcibly fed into a confined passage at the other end of which there is a weighted closure flap which resists the emergence of the tow. Owing to the resistance that the aforementioned closure flap exerts on the emergence of the tow, the fibres or filaments therein take up a crimped or zig-zag formation and are often set in this formation by some form of heat treatment applied subsequent to the crimping operation. This method of imparting crimp to textile fibres is now generally known and referred to as the stufier box process.

The resulting crimped staple fibres, which may be ob tained from the tow of continuous filaments by some suitable cutting technique, can then be spun into a yarn which exhibits a desirable fullness and Warmth of handle similar to that of wool.

In order to increase the permanence and fullness or bulkiness of the yarn obtained from the stutfer box process it has been proposed in United States Patent Number 2,763,898 to subject the tow to some form of relatively mild heat treatment immediately prior to crimping. The heat treatment may comprise passing the tow through a tube either heated electrically or by a heating jacket or the tube may be supplied with steam at atmospheric pressure.

In the past crimped yarns obtained in the above manner have had sufi'icient fullness or bulkiness to satisfy the requirements for the end uses in which they were em ployed. However, with advent of an outlet for fine denier yarns for hand knitting and coarser denier yarns for carpet manufacture there has arisen a demand for ya-rns having a greater bulk and increased resilience.

It is possible to obtain the desired increase in bulk and resilience by providing a greater resistance to the emergence of the-tow from the stulfer box,i.e., by increasing the back pressure. However, such increase in back pressure causes wear on the component parts of the stuiferbox and hence increases the maintenance and running costs. Furthermore, as the back pressure is increased the uniformity of crimp in the tow is decreased to an undesirable extent. Thus this method of obtaining higher bulk is commercially unattractive.

We have now found that the aforementioned improvements in the properties of textile fibres can conveniently be obtained by continuously subjecting a tow of the textile fibres to the action of saturated steam at superatmospheric pressure immediately before crimping. The crimped tow then obtained has a good crimp uniformity.

Accordingly, therefore, the present invention provides a process for the manufacture of crimped tows of thermoplastic textile fibres wherein the tow is subjected to the action of steam at superatmospheric pressure immediately prior tocrimping.

Preferably, the steam at superatmospheric pressure should be wet and the crimped tow should have a crimp frequency greater than 15 and a crimp ratio greater than 30.

The pre-steaming treatment may conveniently be effected by passing the tow through a suitably modified presteaming chamber.

The length of the steam chamber will depend on the rate of travel of the tow and the pressure of the steam employed. It should be sufficiently long to enable the tow to at least attain the equilibrium temperature of the steam. Thus for a 100,000 denier tow travelling at 600 feet per minute and employing a steam pressure of 25 pounds per square inch gauge, (p.s.i.g.), the chamber may be 36 inches long and 4 /2 inches in diameter. The tow is then in the steam chamber for about 0.3 second, 0.15 second of which time is taken in attaining the equilibrium steam temperature (130 C.). The steam chamber is fitted at each end with glands, through which the tow passes and which are designed to maintain the steam pressure within the chamber, together with a steam inlet, a steam trap and drain for removing excess condensate and a pressure gauge. The aforementioned glands may be in the form of sleeves about 4" long and have a diameter which is arranged to be smaller than that of the uncompressed tow'to be treated so that on the passage of that tow through the gland an effective steam seal is obtained. The ends of the glands are preferably flared outwardly in order to facilitate the passage of the tow and to ensure the absence of sharp edges which might cause damage to the fibres or filaments constituting the tow. The effectiveness of the combination of the glands and the tow in providing a steam seal is demonstrated by the fact that a tow having a total denier-of 100,000 may be treated with steam at 24 p.s.i. from a 28 p.s.i. steam linewhen glands having a diameter of 0.19 in. diameter are employed at each end of the steam chamber.

The fullness or bulkiness of a crimped tow is frequently defined by its crimp frequency, that is the mean number of crimps per inch (C.P.I.), assuming a two dimensional zig-zag crimp, measured under defined conditions, e.g., when suspended freely under a load of 1 gm./ 1000 tow denier :25 g. We believe, however, that the more useful definition of bulkiness is obtained by reference also to the crimp ratio of the tow. Crimp ratio is herein defined by being expressed as p 2 l T X where: -L =the length of tow (crimped) when under a load of 1 gm./ 1000 tow denier, $2.5 g., when suspended freely and L =the length of tow (decrimped) when under a load of 1 kg./ 10,000 tow denier 0.5 kg., when suspended freely.

Using crimp ratio as a parameter of bulkiness two tows having the same crimp frequency but different degrees of bulkiness can be differentiated, the tow having the highest crimp ratio being the most bulky. This can be explained by considering two tows having the same crimp frequency but different crimp ratios. The tow with the smaller crimp ratio will have a relatively large crimp angle and crimp leg length and will thus exhibit a flat crimp. In contrast the tow having the higher crimp ratio will have a smaller crimp angle and longer crimp leg length and therefore will have more yarn per unit length of crimped tow and will be the most bulky.

It has been observed that the crimp ratio of a tow of polyhexamethylene adipamide filaments increases slightly with time after crimping to reach a maximum after about 5 hours, this is known as the lagging time. Since also the crimped tow has to be steam set after crimping and it is known that this causes a reduction in crimp ratio and crimp frequency, the amount of the reduction depending of the pressure of steam employed in steam setting, it follows that these parameters should be measured after lagging but before steam setting.

This invention also includes apparatus for treating textile fibres with steam at superatmospheric pressure, the modified steam chamber previously described herein being an example of such an apparatus.

The increased bulk, as shown by crimp frequency and crimp ratio determinations, obtained in textile fibres when employing the process of this invention and the apparatus hereinbefore described is illustrated by the following examples, which examples are in no way intended to limit the scope of the invention.

Example 1 Samples of 100,000 denier continuous filament tows of drawn 6 denier per filament (d.p.f.) polyhexamethylene adipamide moving at 600 f.p.m. are subjected to a presteaming treatment using steam pressures in the range to 15 p.s.i.g., immediately prior to conventional stuiferbox crimping. After crimping the tows are collected by coiling into a bag and then lagged for 5 hours before crimp ratio and crimp frequency determinations are carried out. Subsequently, the tows are steam set in a Sanderson cabinet at 25 p.s.i.g. The values of crimp ratio and crimp frequency obtained after lagging but before steam setting and the crimp ratio after steam setting are quoted in Table I.

Table I shows that the crimp ratio and the crimp frequency increases as the steam pressure in the pre-steaming chamber is increased.

The steam set tows are cut into staple fibres and spun into yarns which exhibit increased bulkiness and resilience as the crimp ratio of the tow from which the yarns originate increases.

In order to obtain the maximum benefit from the action of steam at superatmospheric pressure on a tow of synthetic thermoplastic filaments it is highly desirable that the steam should be wet and not dry. An increase in crimp ratio is observed when dry steam is used but it is less than half of that observed when wet steam is used, as shown in the Table II below.

The increase in bulkiness and resilience of ya-rns spun from tows processed according to this invention can be illustrated by reference to the percentage increase in specific volume and elastic recovery of yarns spun from 6 d.p.f. staple fibres obtained from tows processed according to this invention compared with standard 6 d.p.f.

4 staple fibres The relevant figures are given in the Table III.

TABLE III Percent in- Percent in- Crimp Ratio crease in crease in specific elastic volume recovery Standard 6 d.p.f. staple fibre yarn 18 Staple fibre yarn from towtow pre-steamed with 5 p.s.i.g. steam 38 17 53 Example II A 100,000 denier 6 d.p.f. continuous filament polyethylene terephthal ate drawn cow was subjected to a wet steam treatment at 15 p.s.i.g. in a pre-steamer immediately before stutter box crimping at a speed of 350 f.p.m. and subsequently steam set at 25 p.s.i.g. in a Sanderson cabinet in the manner of Example I. The CR1. and crimp ratio are shown in Table IV below and compared with figures obtained for a similar tow which had not been subjected to the action of steam at superatmospheric pressure.

TABLE IV Crimp ratio C.P.I. aft-er Crimp ratio Presteaming after lagging lagging after steam Setting 0 23 12 20 15 p.s.i.g 35 20 35 Yarn spun from staple fibres obtained from the presteamed tow had improved resilience and was more bulky than yarn spun from standard staple fibres.

Example III A 100,000 denier 6 d.p.f. continuous filament Ulstron (Ulstron is the registered trademark of Imperial Chemical Industries Limited for crystalline polypropylene filaments) drawn tow was processed as in Example II and the values of C.P.I. and crimp ratio given in Table V.

TABLE V Crimp ratio C.P.I. after Crimp ratio Pre-stea-ming after lagging lagging after steam setting 0 21 20 16 15 p.s.1 g 40 30 32 Yarns spun from staple fibres obtained from the presteamed tow showed improved bulk and resilience characteristics compared with yarns obtained from normal staple fibres.

An additional advantage in obtaining tows of high crimp ratio by the pre-steaming process of this inven tion is that the loss in crimp ratio in steam setting is reduced with increasing steam-pressures in the pre-stea-ming chamber as shown by the last column in. Table I. Thus if the steam is at atmospheric pressure then there is a 38 percent reduction in crimp ratio after steam setting at 25 p.s.i.g. in a Sanderson cabinet, but if the steam used in the pre steamer is at 15 p.s.i.g. the reduction in crimp ratio is only 24 percent on subsequent steam setting.

In order to obtain the maximum benefit from the process of this invention care should be taken to ensure that the steam pressure in the pre-steaming chamber is lower than that at which the tow will be subsequently steam set. If the steam pressure in the pre-stea-ming chamber is higher than the steam setting pressure the crimp in the tow will not be fully set and will tend to be lost in subsequent processes involving the use of steam or hot water, e.g., in dyeing.

Although the examples contained herein refer only to 6 d.p.f. tows of thermoplastic filaments, the process may be equally applied to tows of high and lower filament denier. Thus 3 d.p.f. crimped to-ws may be treated according to this invention and subsequently converted, for example, into hand knitting yarns which have a high bulk and pleasing handle. Fabrics knitted from these yarns display a desirably high degree of resilience and bulkiness, have a warm handle and are less prone to pilling than comparable fabrics knitted from standard staple fibre yarns.

Tows having a higher filament denier, e.g., 12 d.p.f., which have been treated according to this invention are particularly suitable for conversion into carpet yarns. The improved resilience and bulk of these yarns enable carpets to be manufactured with a low pile weight Without loss in performance of the carpet. Such carpets have a pleasing appearance and are crush resistant.

The invention may be applied to tows of thermoplastic filaments which have any desired cross-section, e.g., trilobal.

What we claim is:

1. A process for the manufacture of crimped tows of thermoplastic fibres having a crimp frequency greater than 15 and a crimp ratio greater than 30, said process comprising subjecting the tow to the action of wet steam at superatmospheric pressure for a period suflicient for the tow to attain substantial equilibrium temperature with the steam, immediately crimping the tow in a stuffer-box, and steam-setting the tow at a higher steam pressure than the pressure at which the tow was steamed prior to entry into the stutter-box.

2. A process as in claim 1 wherein the tow is subjected to said wet steam for a period of time beyond that required to raise the equilibrium temperature of the temperature of the tow to the steam.

References Cited by the Examiner UNITED STATES PATENTS 2,575,781 11/1951 Barach 2872 2,686,339 8/1954 Holt 2872 2,888,733 6/ 1959 Wegener 2872 3,031,734 5/1962 Pike 2872 3,036,357 5/1962 Cook et a1. 2872 3,037,260 6/1962 Pike 281 3,152,379 10/1964 Osban 2872 FRANK J. COHEN, Primary Examiner. STANLEY N. GILREATH, Examiner. J. PETRAKES, Assistant Examiner. 

1.A PROCESS FOR THE MANUFACTURE OF CRIMPED TOWS OF THERMOPLASTIC FIBRES HAVING A CRIMP FREQUENCY GREATER THAN 15 AND A CRIMP RATIO GREATER THAN 30, SAID PROCESS COMPRISING SUBJECTING THE TWO TO THE ACTION OF WET STEAM AT SUPERATMOSPHERIC PRESSURE FOR A PERIOD SUFFICIENT FOR THE TOW TO ATTAIN SUBSTANTIAL EQUILIBRIUM TEMPERATURE WITH THE STEAM, IMMEDIATELY CRIMPING THE TOW IN A STUFFER-BOX, AND STEAM-SETTING THE TOW AT A HIGHER STEAM PRESSURE THAN THE PRESSURE AT WHICH THE TOW WAS STEAMED PRIOR TO ENTRY INTO THE STUFFER-BOX. 